A fuel cell which uses a solid high-molecular membrane as an electrolyte membrane comprises a pair of electrodes arranged so as to sandwich the solid high-molecular membrane, and is configured such that fuel gas such as hydrogen is supplied to a surface of one electrode and oxide gas containing oxygen is supplied to the other electrode, thereby obtaining electric energy. FIG. 5 is a cross sectional view showing a configuration of such a conventional fuel cell. Referring to FIG. 5, an anode 12 which is a hydrogen electrode and a cathode 14 which is an oxygen electrode are disposed on respective sides of an electrolyte membrane 10. Charge collectors 16 are further provided on the outer surfaces of the anode 12 and the cathode 14, respectively, and these charge collectors 16 are then sandwiched by a pair of separators 18.
In order to achieve excellent electrical conductivity, the solid high-molecular membrane used as the electrolyte membrane 10 needs to contain sufficient water for realizing a wet condition. Accordingly, a method has been typically used in which hydrogen to be supplied to the anode 12 and oxide gas such as air to be supplied to the cathode 14 is humidified before being supplied to the fuel cell. In the example shown in FIG. 5, hydrogen to be supplied to the anode 12 is humidified.
However, the conventional fuel cell using a solid high-molecular membrane as described above may suffer from a so-called flooding phenomenon, in which moisture used for humidification is condensed inside pores of the anode 12 which is a hydrogen electrode and of the charge collectors 16 to plug the pores, thereby causing non-uniform flow of hydrogen, as shown in FIG. 6. In such a state, supply of hydrogen is concentrated only in specified portions, where the current density is increased, leading to a problem that the electrolyte membrane 10 would tear. This problem is similarly caused when air which is oxide gas to be supplied to the cathode 14 is humidified.
In order to eliminate the above flooding phenomenon, a method has been proposed, as disclosed in Japanese Patent Laid-Open publication No. 2000-251912, in which a supply tube for gas such as hydrogen or air to be supplied to the fuel cell is heated to thereby reduce condensation of moisture used for humidification.
When the gas supply tube is heated, however, the temperature of the gas to be supplied also increases, and when the heated gas comes into contact with the entire surface of the solid high-molecular membrane, the whole membrane is heated and deteriorates easily.